The trichloromethyl group is a
functional group that has the
formula –CCl3. The naming of is group is derived from the
methyl group (which has the formula –CH3), by replacing each
hydrogen atom by a
chlorine atom. Compounds with this group are a subclass of the
organochlorines. Some notable examples of compounds with this group are
trichloromethane H–CCl
3,
1,1,1-trichloroethane H
3C–CCl
3, and
chloral HOC–CCl
3.
The trichloromethyl group has a significant
electronegativity.[
citation needed] For this reason, trichloromethyl-substituted acids, such as
trichloromethanesulfonic acid, are often stronger than the original. For example, the
acidity constant (pKa) of
trichloroacetic acid HOOC–CCl
3 is 0.77, whereas that of
acetic acid is 4.76.
[1]
[2]
By the same principle, the trichloromethyl group generally lowers the basicity of organic compounds, e.g. trichloroethanol.